Title: The Power To Cast Out Demons

Rating: K+

Summary: Remus Lupin recognises the similarity between a story Dumbledore tells him, and something that's going on in his own life. Set at the end of HBP.

Disclaimer: I don't own the Harry Potter world or its characters. J. K. Rowling does.

"Well, there are ghosts," said Nearly Headless Nick, "and there are the majority who go straight on to the next stage, whatever that is."

"And no other options?" Remus asked insistently.

Nick hesitated, then answered with some reluctance, "There is one. It involves stealing someone else's life. I don't know how to do it, and I wouldn't if I did know. Neither would Sirius, nor Dumbledore, if you're thinking about them."

"No, I'm not thinking about them. Isn't there anything more you can tell me?"

"Not much. As I said, I don't know how it's done. But the dying person – and it has to be a wizard or witch, of course – somehow projects himself into the body of a living person and takes it over."

"So the host body would have to be someone who was alive at the time of the wizard or witch's death?"

"It looks like it. I don't know for sure. The Bloody Baron probably knows more. He knows more than me about most things. But he's not in a very co-operative mood at the moment, so I doubt if you'd get much out of him. The man to ask would have been Snape, if he hadn't taken off. Have a rummage in the Restricted Section of the library, that's your best bet, or chat to someone who's into the Dark Arts."

Remus thanked Nick, and left in search of Horace Slughorn, stopping off at the kitchen where he found an elderly house-elf who remembered him from his Marauder days, and was delighted to provide him with a bag of crystallised pineapple, when Remus had explained what that was.

Slughorn accepted the gift graciously, querying: "What can I do for you? Because you're after something, and I don't think it's my body."

"No, it never was, was it?" Remus laughed. "Just a little information, that's all. About a spell that would enable a dying wizard to live again in someone else's body."

"No such spell exists," Slughorn said ponderously, but not before Remus had observed a quick flash of curiosity in his face.

"I have it on good authority that it does, and that in the absence of Snape and Dumbledore, you are the man most likely to possess knowledge of it," Remus said.

"If there were such a spell," Slughorn began, speaking slowly and carefully, "which there isn't – but if there were, it could only be employed by one who was not only very knowledgeable in the Dark Arts, but also completely unscrupulous. It amounts to robbing someone of his life – to murder, in fact. May I ask what your interest in this matter is?"

"I believe a friend of mine has become a victim of it," Remus answered.

"I am very sorry to hear it," said Slughorn. "May I ask who the victim is?"

Remus told him.

"Tragic," said Slughorn, shaking his head. He appeared to have dropped the pretence of ignorance about the spell, and Remus felt encouraged to question him further.

"I wondered if you could tell me what happens to the soul of the victim?" he asked. "Does it proceed to the state of death?"

"No. It remains with its body, able to see, hear and feel everything that happens to its body, but incapable of independent speech or movement. It is as if all its motor nerves have been cut, while its sensory nerves still function. A very terrible situation to be in."

Remus was silent for a moment, contemplating the horror of what Slughorn had told him. To be a helpless prisoner in one's own body, looking on while another's will forced it to abhorrent actions – death would surely be preferable. But there was still a chance that it hadn't happened.

"I suppose," Remus asked, "that the victim would have to be in the vicinity at the time of the perpetrator's death?"

"Not at all," Slughorn replied, seeming now eager to impart his knowledge. "The dying wizard projects his soul into a nearby object……"

"Like a Horcrux?" Remus interrupted.

"Not exactly. There is no splitting of the soul. It transfers whole into the object selected. There it remains, fully conscious and with all its former mental and magical faculties intact, until it comes into contact with a suitable host. It then enslaves the host's body, leaving his – or her – soul an unwilling observer of its life, instead of an active participant."

An inanimate object. Not something like a book, or an article of clothing, thought Remus, too easily destroyed. Something durable, of metal or stone maybe. Something that would last for years, passing from hand to hand, until it reached the person whose body was to be taken over. Something of value, that wouldn't be thrown away; a piece of jewellery perhaps, a watch or a ring.

"Then this object would be charmed, in preparation to accept the dying soul, so that at the moment of death the soul would move into it?" Remus asked.

"That's how I imagine it must work," replied Slughorn.

"And is there any way of ejecting the usurper?"

Slughorn was silent for so long that Remus thought he was going to refuse to answer. At last he said hesitantly, "Any attempt would have to be made on the spiritual plane."

"Have you ever tried?"

"No. And it would certainly be beyond the ability of any single wizard, however powerful. Two or three, at least……"

"Then you'll help me?"

Slughorn looked shocked. "Certainly not. For any living person to venture onto the spiritual plane is a desperately dangerous enterprise. One might not get back, one could be lost……no, I will not attempt it and I advise you not to either."

"But I must do anything I can to help a comrade of the Order, and one who is kin to my lover. And the truth is I can have no peace in my own life until this matter is resolved."

"Then I will give you the spell, and the potion which you will need. And I will suggest a wizard and witch who might be glad to accompany you. But I will not."

"Oh, come, Horace, it will be a fine adventure. Let me bribe you – not with crystallised pineapple, no, with werewolf teeth. At the next full moon, I'll take Wolfsbane Potion and be a tame little puppy dog, and you can immobilise me and draw out as many of my teeth as you wish. They will remain wolf teeth after I have regained my man shape, and you know what strong magic they have."

"You would do that?"

"I would."

"It's been my dream to own a werewolf tooth. One is all I need. I could……all right, I'm with you."

-oo000oo-

Remus paced the path leading to Hagrid's hut, lost in thought. He had left the preparation of the venue to Slughorn, in no doubt that it would be meticulously done, but he had slight doubts about the choice of their helpers. Left to himself, Remus would have chosen Alastor and Minerva, the strongest witch and wizard he knew, but on the other hand, Slughorn's two were highly motivated, which could more than make up for whatever they might lack in magical power.

"Wotcher! You busy?" Tonks appeared at his side, smiling cheerfully.

"No, as a matter of fact I'm rather at a loose end," Remus answered. "Now that I can't go back to Fenrir and the werewolves, I'm on general patrols until Alastor thinks of something else to do with me, and I've just come off duty."

"Great, I'm free too, so we can go off somewhere for a quiet chat."

"All right. I know just the place, where we won't be disturbed."

When he told her, her eyes widened in shock. "But it's full of ghosts!" she exclaimed.

He laughed. "No it isn't." On the way there he told her about the history of the Shrieking Shack. "And now you're one of the very few people who know how to stop the Willow from Whomping."

"Oh don't worry, I shan't tell anyone," she said. "I like learning secrets, and I know how to keep them to myself."

Inside the upper room, she looked around, impressed.

"It's really nice here!" she said in surprise.

"Yes, it's been refurbished since the time when I used to rampage about breaking up the place," Remus said with a smile. "Come and sit down."

They sat on a small two-seater sofa, upholstered in red fabric which clashed horribly with Tonks's hair. She slid an arm around his shoulders and leaned her head against him. "What d'you think about Christmas?" she asked.

"Er – on balance, I'm in favour of it," he replied.

She grinned. "I mean, as a time for us to get married."

"I don't think so. You see, I know you."

"Well, I should think you do. We've been working together for about two years. And now it's time to get to know each other a lot better." She raised her face to his.

"No, I mean I really know you. I know who you are, Merope Riddle."

"What are you talking about? You gone mad? Who is this Merpy wossname?"

"Nice try, Merope, but it won't work. Dumbledore told me all about you, about your obsession with Tom Riddle, and everything fell into place. I'd known for some time that Tonks wasn't herself, and now I see that she literally isn't herself."

"You're talking nonsense. People change when they fall in love, that's all it is. I'm still me. Merope's dead these seventy years."

"You sure about that? Because a minute ago you made out you didn't even know who she was."

"Very clever, trying to trap me. But I'm Tonks, I love you, I want to marry you, and I won't take no for an answer."

"Stop being stubborn and face the facts. What you're doing is wrong. You're taking the life of an innocent woman who has never done you any harm. I know you had a hard life, and things happened to you that were unjust, but you can't make it right by stealing someone else's life. Leave her now, and go to wherever you ought to be."

"No. This body that I have won is better than the body I had in life. It's stronger and its face is more pleasing, and I've learned to use its rare ability. I'm holding on to what I have. And you can share in my triumph, Remus Lupin. I love you for the beautiful darkness that is in you, even though you reject it. I will teach you to rejoice in it. You've been a fool, you've fought on the losing side, but I love you nonetheless, and my son will forgive you for my sake. Together we will rule half the world under Him. And when the moon rises an unbroken circle, you will make me as yourself, and we will revel in blood and slaughter which makes His heart glad, and He will love us."

Remus felt intense pity for Merope, but reminding himself of how Tonks must hate to hear this talk of blood and slaughter from her own mouth, he pushed her away and sprang up. This was the signal for the other three to come out from the shadows in the corners of the room: Slughorn, Andromeda and Ted Tonks, vials of potion in their hands. Ted and Andromeda seized hold of Tonks. Slughorn pushed a vial at Remus, and the four of them drank, saying in unison: "Excorporeo".

Remus felt a dizzy sensation; he seemed first to be moving in a spiral, then to stand motionless while the world spun around him. Unidentifiable shapes and dazzling colours flashed before his eyes while discordant sounds assailed his ears. At length he felt himself falling, falling through dark empty space for what seemed like an impossibly long time. It was an unpleasant feeling, much worse than taking a Portkey. With relief at last he felt solid ground under his feet, and found himself in a room very different from the one in the Shrieking Shack he had left. It was round, with white walls and two round windows looking out to a black, starry sky. It was empty of furniture. On the red-carpeted floor Tonks lay, supported by Ted who was holding her jaws open while Andromeda forced her to drink the contents of another vial. Slughorn was there too, but Slughorn as Remus had never seen him; young, slim and handsome, barely recognisable as the corpulent professor of a few moments before. Briefly, Remus wondered if his own appearance had similarly changed; but there was no time to ponder about that because Merope had come out of Tonks's body and was standing before him.

"You fool!" she hissed, "you dare to defy me! You could have had the world……but now you will suffer, until you recognise where your own best interests lie."

Remus had not known that it was possible to perform the Cruciatus curse without a wand, but he now learned that Merope, at least, could do it. Incapacitated by pain, he saw Slughorn move to take up a position between Tonks and Merope. Ted and Andromeda stood with him, and the three were fully occupied in deflecting Merope's curses.

Remus dragged himself across the floor to where Tonks lay unconscious. Her right arm was flung out by her side, and on her finger was a silver ring set with three emeralds.

"Where did she get the ring?" he called to Andromeda.

Andromeda replied, without taking her eyes from her enemy and without ceasing to defend herself from Merope's attack. "Me – bought it for her last year – second-hand – Knockturn Alley."

Remus drew the ring from Tonks's finger, but before he could examine it, it was pulled from his grasp and flew across the room towards Merope, who with a triumphant smile held her hand out to receive it.

"I'll take that," said a voice. The ring halted in mid-air just before it reached Merope's outstretched fingers, and made a right-angle turn into Dumbledore's hand.

Merope screamed "Tom! Come! Help me!"

"He will not help you," Dumbledore said gravely. "You have failed him, and he will leave you to your fate. Surely you know his nature?"

Merope shrank back against the wall. Tonks opened her eyes and moaned. Andromeda rushed to her side. Remus stood up shakily, and said "I thought you were dead. Are you a ghost?"

Dumbledore smiled. "I am not a ghost. I am alive in the spirit world, and you can see me because you, too, are temporarily in the spirit. But it is time for you to return to the earthly plane. Andromeda, Ted, your daughter is herself again. Take her home."

The three Tonkses joined hands and spoke the word that returned them to the world and made them vanish from Remus's sight.

Dumbledore held out his hand towards the trembling spirit-woman. "Come, Merope," he said gently.

Merope remained motionless, terror in her eyes.

"Don't be afraid," said Dumbledore. "Life has dealt cruelly with you. You should be glad to leave it. I am going to a place of rest, renewal and hope. Come with me, and find what you need."

Slowly, timidly, Merope came forward. Dumbledore grasped her hand and drew her behind him. Turning to Remus and Slughorn, he said "You have done well. I am very proud of all of you," before he and Merope disappeared.

"I'm proud of you too," said another voice, a heart-stoppingly familiar one. Sirius was negligently leaning against the wall between the two round windows, looking unbearably handsome and young. Remus started gabbling, the questions pouring incoherently out of him.

"Sirius! Is it you? How are you? Where are you? How are things where you are? Is it……are you……what……how……"

Sirius's smile broadened. "I'm well," he said. "I'm in a good place. I'm with James and Lily, and they send you their love. When I heard you were here, I couldn't resist coming to see you. Thanks for saving my little cousin. Thank you too, Professor Slughorn. I never had you down for a hero, and I apologise. It's good to see you both. But you have to go now."

"Can't I stay with you?" Remus asked, though he knew the answer.

"Not now. When your time comes, we'll be together. I'll be waiting for you."

Remus bowed his head in resignation.

"Do something for me," said Sirius.

Remus looked up. "Anything," he said eagerly.

"Live your life. Don't just drag it out waiting to die. Be happy. Have fun."

"I will," Remus whispered, and Sirius vanished.

Remus and Slughorn turned to each other, both smiling ruefully, for different reasons.

"Time to go back to being the fat old Professor," said Slughorn.

"I'd quite forgotten I was ever this slim. Tell me, am I good-looking too?"

"Yes," Remus said, still smiling. In spite of everything, he was happy. Nothing else mattered, not even a hundred years' wait, now he knew Sirius was alive, and still loved him. Not that he had ever seriously doubted either, but it was good to know for certain.

The return journey was shorter and less hair-raising, and the Tonkses were still in the Shrieking Shack when Remus and Slughorn arrived. Tonks was stretching out her arms, flexing her fingers, shaking her head and sending her long, straight, lime-green hair floating around it. Andromeda was muttering something about never again buying anything second-hand without giving it a thorough check for charms, curses, and undead souls.

"It feels great to be back," Tonks said. "Thank you all so much. I owe you big time."

"A debt which can happily never be repaid," said Slughorn.

Only Remus knew the source of the quotation, but they all laughed before making their way home.

A/N Yes, I know, huge gaping plot-hole: why did Dumbledore tell Remus about Merope and her obsession with Tom Riddle senior? Well, he did, that's all. He wanted to talk about it to someone older than Harry, and he suspected that his usual confidante, McGonagall, would have taken Merope's side and used the occasion to point out how cruel and unfeeling men were.